This invention relates to an improved construction of a liquid crystal display cell and more particularly to a liquid crystal display cell in which the liquid crystal is filled into the cell through an inlet port or opening provided for a peripheral sealing member which supports and secures spaced glass plates of the cell and the inlet port is hermetically sealed by an inlet port sealing member.
A liquid crystal display cell generally comprises a pair of spaced insulating plates such as glass plates which are hermetically secured to a peripheral sealing member provided with an inlet port for filling the liquid crystal. The profile of the peripheral sealing member is defined on a glass plate by a silk-screen printing machine in a general manner. However, in a small liquid crystal display cell for use in small timepieces for example, the spacing between the glass plates is only 6 to 10 microns so that the width of the inlet port provided through the side surface of the peripheral sealing member inserted in such small spacing is less than 1 mm. Accordingly, care should be taken not to close or decrease the area of the inlet port during assembly of the cell, and it is generally difficult to secure the glass plates to the peripheral sealing member with the peripheries of the glass plates and the periphery of the peripheral sealing member being flush with each other. Sometimes the peripheral portions of the glass plates project about 4 to 20 microns beyond the periphery of the peripheral sealing member.
FIG. 1a shows a plan view and FIG. 1b a side view of a liquid crystal display cell in which the glass plates project beyond the periphery of the peripheral sealing member and the inlet port for filling the liquid crystal is not yet sealed.
As shown, the cell comprises a pair of glass plates 1 and 2 secured to the opposite surfaces of a peripheral sealing member 3 made of low melting point glass, for example. Liquid crystal and display electrodes (not shown) are housed in the cell. An inlet port 4 for filling the liquid crystal into the cell is provided through a portion of the peripheral sealing member between the glass plates.
FIG. 2 shows some examples of the prior art inlet port sealing member for sealing the inlet port of a cell in which the peripheries of the glass plates project beyond the periphery of the peripheral sealing member. According to one example shown in FIGS. 2a and 2b, a metal layer 5 is formed on the portion of the glass plates about the inlet port by, for example, vapour deposition or ion plating and a solder 6 is applied onto the metal layer 5 for sealing the inlet port 4. Of course, the joints between the glass plates and the peripheral sealing member other than the inlet port are hermetically sealed by the adhesion of the peripheral sealing member made of low melting glass.
In this construction, since the metal layer 5 is formed prior to the assembly of the glass plates and the peripheral sealing member, the portions of the peripheral sealing member 3 about the inlet port 4 is not formed with a metal layer and after application of the inlet port sealing member or solder, a fine passage 9 having a depth of 4 to 20 microns is formed along the outer surface of the peripheral sealing member 3 and between the plates. Accordingly, it has been necessary to seal the opposite ends of the passage 9. If low melting point glass is used for this purpose it is necessary to heat the cell and such heating deteriorates the liquid crystal. For this reason, room temperature setting type organic resins have been used as the sealing agent.
However, room temperature setting type sealing agents have a higher tendency to chemically react with the liquid crystal than other inorganic sealing agents such as low melting glass and solder. Moreover, since the organic sealing agents do not have properties for preventing humidity in the ambient atmosphere from passing therethrough, the liquid crystal quickly deteriorates due to hydrolysis. Further, their resistance to weather, ultraviolet ray, for example, is low. To solve these difficulties it has been proposed to apply a metal layer 5a to surround the inlet port 4, on both glass plates 1 and 2 and the peripheral sealing member 3, as shown in FIGS. 2c and 2d. However, due to offset relationship between the glass plates and the peripheral member it has been difficult to form a continuous metal layer to completely cover the side surfaces of the glass plates and the peripheral sealing member so as to eliminate passage 9.